-LRB- CNN -RRB- -- Last week , the Internet was buzzing with the news that a DNA test of white supremacist Craig Cobb revealed that 14 % of his genes originated in sub-Saharan Africa .

The look on Cobb 's face as he received the news ? Priceless .

Cobb appeared on `` The Trisha Show '' and discussed his plans to create an all-white town for white supremacists in Leith , North Dakota .

`` Whites are the highest expression of DNA on the planet , '' he said on the show .

When Cobb received the DNA results , he wrote it off .

`` This is called statistical noise , '' Cobb responded . `` Oil and water do n't mix . ''

Well , apparently we are n't talking oil and water , are we Mr. Cobb ? We 're talking human beings -- and they 've been mixing since the beginning of time .

That history is what created the `` one-drop rule '' in America : a legal classification that held that anyone with as little as `` one drop '' of African or black ancestry was to be categorized as black and treated accordingly . Until 1967 , when it was ruled unconstitutional , the `` one-drop rule '' provided the legal and quantitative definition of blackness , and whiteness .

So while Cobb might `` look white '' today , in 1813 or 1913 , his 14 % African ancestry would have been more than enough to render him black by law . In 2013 , however , the irony of his heritage shows just how nuanced racial identity is beyond skin color .

During the period of American slavery , 1619 to 1865 , freedom was predicated on skin color . If you were white , you were free ; if you were black , you were enslaved .

But this simple social order soon became complicated by miscegenation ; and with the rampant increase in racial mixing , the lines between white and black , free and enslaved , became more and more blurred .

Whites were afraid of losing their control over the enslaved population . They needed to maintain a firm color line . So , state governments began instituting anti-miscegenation laws . Various and varying articulations of the `` one-drop rule '' emerged : a classification that held that anyone from 1/8 to 1/16 to 1/32 to any known trace of African or black ancestry was to be categorized as black and treated accordingly . How that `` drop '' was measured varied from state to state .

The rhetoric of white supremacy not only argued that the races were distinctly different , but also that the black race specifically was inferior , therefore justifying enslavement . Mixing , then , lowered human quality .

In order to maintain its superiority , whiteness had to remain pure . So , what it meant to be white was to be free of `` otherness '' in general , blackness , specifically . In this way , miscegenation was a threat to the survival of the white race . The `` one-drop rule , '' then , became critical in its defense .

To be white in America was to be `` pure . ''

Or was it ?

A 2002 study of racial admixture conducted by Penn State University molecular anthropologist Mark Shriver showed that among those who self-identify as white , upward of 30 % have at least 2.3 % African ancestry -- the equivalent of having had three black ancestors somewhere within the previous five generations of their family .

What that means , then , is that 30 % of the folks who call themselves white have much more than one drop , including white supremacist Craig Cobb .

DNA testing also reveals that somewhere around 60 % of black Americans have white ancestry , Shriver 's study found .

Taken together , it 's clear that racial purity is as much a delusion as white supremacy .

Blood does not define identity .

Although the `` one-drop rule '' in many ways serves foundational to black American racial identity , and has functioned to draw borders around the black community as we know it , one drop of `` blackness '' -- whatever that is -- does not constitute black identity .

Blackness , as an identity and as a lived experience , is much more complex and nuanced than any number of drops on a family tree . Blackness is as much about who creates you as it is about what you make of yourself .

So , while I was thoroughly amused by the sight of Craig Cobb 's face when he learned that he , too , is `` of African descent , '' I am clear that those DNA test results do not magically make him black ; no number of drops ever could .

And blackness is too beautiful to be forced upon people who do n't want it . So no worries , Mr. Cobb , your secret 's safe with me .

The opinions expressed in this commentary are solely those of Yaba Blay .

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White supremacist Craig Cobb learned that 14 % of his genes originated in sub-Saharan Africa

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That would make him legally `` black '' under America 's one-drop rule , Yaba Blay says

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The `` one-drop rule '' provided the legal and quantitative definition of blackness , and whiteness

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Blay : Irony of Cobb 's heritage shows how nuanced racial identity is beyond skin color